Recent experimental progress in developing methods for fabricating strictly 2D crystals that were previously believed to be thermodynamically unstable have lead to remarkable paradigm-shifting discoveries in solid state physics. Graphene, a single layer of graphite, has attracted tremendous interest from the scientific community owing to its remarkable properties such as the room-temperature half-integer quantum Hall effect, the massless Dirac fermion nature and extremely high mobilities of its charge carriers, the tunability of its band gap (for graphene nanoribbons), and the potential for realizing ballistic conduction. Graphene also possesses fascinating thermal and mechanical properties, which make it an attractive candidate for potential applications such as in electromechanical resonators, stretchable and elastic matrices for flexible electronic circuitry, stable field emitters, ultracapacitors, and as fillers for electrically conducting flexible nanocomposites.
The fabrication of large-area graphene represents a formidable challenge that must be overcome to realize the potential of this material, although some progress has been achieved very recently using chemical vapor deposition and epitaxial growth methods. Several approaches have been reported for obtaining single graphene sheets on substrates including the original micromechanical cleavage “scotch tape” method involving the repeated exfoliation of graphite mesas; however, this method gives a very low yield of typically sub-100 μm graphene flakes masked by hundreds of thicker flakes of graphite and is thus unsuitable for precise positioning of graphene structures within device architectures and for scaling to practical quantities. Alternative approaches that have recently been reported include epitaxial growth on SiC and the chemical vapor deposition of CH4 over nickel catalysts. High mobilities for graphene nanoribbons with lateral dimensions <10 nm have been obtained by the chemical exfoliation of commercial graphite using forming gas followed by surfactant-assisted dispersion in non-polar solvents. The obtained nanoribbons are semiconducting and exhibit on/off ratios as high as 107. Solution-chemistry-based approaches involving the initial oxidation of graphite to graphite oxide, followed subsequently by the mechanochemical or thermal exfoliation of graphite oxide to graphene oxide sheets, and their eventual reduction to graphene have also attracted much attention owing to the facile scalability and high yields obtained for these processes.